Vanquiz, any chance you'd be able and willing to post a photo of your device viewing the 12pt version of the PDF? One of the pages in the chapters already (as opposed to the title page or copyright page)?
Your explanation did not yield me any clues as to what could cause what you describe... unless somehow you are actually viewing material at 12 pt fonts, despite your preference setting of 9pt...
If you can, thanks in advance! If you cannot--I shall have to learn to live with this mystery.
